The present invention is generally directed to molds and molding processes, and more particularly to a method and an apparatus for molding processes that utilize an anisotropic diffuser member for uniformly distributing heat within a mold die.
The processing of molded materials is a precise operation requiring the precisely timed application of pressure and the application of precise and uniform temperature. Any deviation from the desired parameters often leads to cracks and/or poor resin flow in the resulting product.
The background art includes several examples of related control schemes for regulating mold process temperatures. For example, U.S. Pat. No. 3,933,335 to Maruyama et al. describes a casting mold for casting metals that includes a paper-like sheet of carbon fibers admixed with organic fibers or pulp that is used as a liner between the molten metals within the mold and the mold""s interior surface. The carbon fiber sheets include at least 35 percent by weight of carbon fibers in order to prevent undesirable stresses and seizure as a result of contact between the molten metal and the interior surface of the mold.
U.S. Pat. No. 4,388,068 to Suh et al., the entirety of which is herein incorporated by reference, describes an injection molding device and method that includes the use of a variable conductance heat pipe for controlling the rate of cooling of portions of a mold cavity surface separately and independently from other portions of the mold cavity surface. This molding device and method inherently relies upon individualized, active temperature regulation and temperature approximation of numerous sub portions at various locations of the mold.
U.S. Pat. No. 5,154,221 to Vatant et al. describes a device for fixing and cooling a graphite block of a graphite wall of a mold. A mold cavity is formed by a plurality of vertically oriented graphite blocks that make up the mold cavity walls. The individual graphite blocks contain vertical bores arranged in parallel to the surface of the mold cavity walls. Each of the bores permits sprayed jet(s) of cooling fluid into the interior of the blocks to effect cooling of the mold cavities. However, the device of Vatant et al. requires a system for collection and delivery of cooling fluid and/or additional machining of parts to create the vertical bores of each graphite block and cooling system.
U.S. Pat. Nos. 5,609,922; 5,746,966; and 5,783,259, all to McDonald, describe methods and molds for molding processes that incorporate thermal coatings applied to an interior surface of a mold cavity via the use of a thermal spray. The coatings may include ceramics, metal matrix composites, ceramic matrix composites, resins and various combinations thereof. The thermal coating is selected to impart a desired porosity into the interior surface of the mold cavity that will aid in rapid cooling and will add to the structural strength of the mold itself. However, the methods and devices of McDonald rely upon precision manufacturing techniques that necessitate controlled thermal spraying of coatings onto mold cavity components of various sizes and shapes.
U.S. Pat. No. 5,811,135 to Kimura, the entirety of which is herein incorporated by reference, describes a molding apparatus having a conventional molding box structure with a thermally expanding member. FIG. 1 is a side view of a molding apparatus according to the background art. FIG. 2 is a front elevation view of a mold member for the molding apparatus of FIG. 1. FIG. 3 is an exploded perspective view of the mold member for the molding apparatus of FIG. 1. FIG. 4 is a sectional view of a molten material filling mechanism for a molding apparatus according to the background art.
As seen in FIG. 1 through FIG. 4, a molding box structure 10 includes horizontally arranged support elements 11, threaded struts 12, and a plurality of nuts 13. A mold member 20 (shown in two parts, e.g., an upper half 21 and a lower half 22), a pressurizing plate 30, a thermally expanding member 40 and an auxiliary pressurizing mechanism 50 are vertically arranged between the lower two support elements 11 in this order from top to bottom. The thermally expanding member 40 includes a temperature adjusting mechanism 60.
The temperature adjusting mechanism 60 is used to control the pressure that the thermally expanding member 40 imparts to the mold member 20 to sealingly engage the upper and lower halves 21,22 of the mold member. The temperature adjusting mechanism 60 also includes a cylindrical heater (not shown) for heating and expanding the thermal expansion member 40. A cooling oil circuit (not shown) is used to contract and cool the thermally expanding member 40.
During a conventional molding process, the mold member 20 is accommodated between the pressurizing plate 30 and one of the support elements 11a2. The upper and lower molds 21 and 22 have concavities formed in faces opposed to each other, in predetermined configurations, respectively. Each of the molds 21 and 22 further has a plurality of positioning pins 23 for preventing lateral misalignment. The upper mold 21 has a material filling hole 21a formed therethrough to correspond to the central cylinder hole 71 formed through the support plate 11a, as shown in FIG. 4.
A thrusting piston 72 is insertable into the cylinder hole 71 and is connected to a piston 73a of an oil-hydraulic cylinder mounted on and extending through a central portion of the uppermost support plate 11b. Movement of the piston 73a vertically moves the thrusting piston 72 so that molten material accommodated in the cylindrical hole 71 can fill the interior of the mold member 20 through the material filling hole 21a of the upper mold 21. Depending on the type of molding process undertaken, the finished molded product is demolded after the required cooling process or molding process is completed.
However, the aforementioned arrangements of the background art lack a simple method for ensuring the elimination of temperature gradients, e.g., hot spots or other temperature variations along variation portions of the mold cavity. These temperature gradients will likely result in surface cracking, sinks, warping and other forms of distortion or surface irregularity. When the mold cavity is heated in an attempt to ensure adequate mold cavity, e.g., the temperature of the melt, the transfer of heat to the mold cavity should be in a controlled, uniform manner that ensures that temperature control does not result in undesirable heating of the melt that may lead to increased mold cooling times and overall process cycle times.
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
The present invention, in part, is a recognition that it will be advantageous to uniformly distribute heat within a mold die or molding cavity during a molding process.
The present invention, in part, is a recognition that the unique properties of fiber reinforced composites can be utilized to produce precision temperature control and heat transfer if manipulated to have a predetermined geometry.
The present invention, in part, provides a mold assembly for a molding process comprising a mold member and an anisotropic diffuser member, the diffuser member comprising a fibrous composite having a plurality of fibers each having a respective length, the fibers being arranged in a lay-up with the length of each fiber arranged in a substantially uniform direction within the diffuser member, wherein the diffuser member is arranged in a position permitting a rapid transfer of heat along the length of each fiber to the mold member.
The present invention, also in part, provides an anisotropic diffuser plate for a mold assembly, the diffuser plate comprising a fibrous composite having a plurality of fibers each having a respective length, the fibers being arranged in a lay-up with the length of each fiber arranged in a substantially uniform direction within the diffuser member, wherein the diffuser member is arranged in a position permitting a rapid transfer of heat along the length of each fiber.
The present invention, also in part, provides a method of controlling process temperatures in a molding apparatus, the method comprising the steps of controlling a temperature of a mold member with a heat source; and arranging an anisotropic diffuser member along a surface of the mold member for distributing heat uniformly along a length of the anisotropic diffuser member.